It could be that your internet is letting you down as well. I had real trouble till I installed leatrix, and now I find mechanics manageable and less difficult. For any fight you are new to, leave your jumps out of rotation until you know when it is safe. In Copperbell HM could it be that you are getting hit by the final boss's 'Power Strike' (<== i think thats what its called) anyways, its a very fast cast and I have never dodged it myself. I don't like to say that marked aoe's are 'impossible' to dodge but that one... i don't know yet how.